editors/nano: Make several port improvements
- Switch to https:// MASTER_SITES
- Use provided .xz for distribution file, saving: 50.5% / 1415kB
- Add LICENSE_FILE
- Remove CPPFLAGS/LDFLAGS variables, added 19 years ago when the port was first created.  They are incorrectly (globally) scoped, no longer necessary and incorrect for the ncurses:base case. Instead use Uses/ncurses.mk variables and provide these to configure to ensure includes/lib searches and linking are never mixed between base and ports.
 ports r29979
Approved by: danilo (maintainer)
MFH: 2019Q2 (blanket: bugfix)